The dramatically escalating number and diversity of older adults are defining features of the world-wide population. Research demonstrates that older adults from marginalized and disadvantaged populations are at elevated risk of accelerated aging and premature death. The National Institutes of Health are committed to reducing and eliminating health disparities and have recognized that health disparities among sexual and gender minority people are one of the main gaps in health research. Recent population-based studies have demonstrated that sexual and gender minority older adults are at elevated risks of chronic health conditions, disability, and poor physical and mental health-related quality of life (HRQOL). The proposed longitudinal research will follow more than 2,300 demographically diverse LGBT adults aged 50 or older recruited from all U.S. Census divisions. Based on an innovative health equity promotion framework incorporating a life course development perspective, this study will examine the risk and protective factors affecting the health and well- being of LGBT older adults over time. This multidisciplinary national research team, in collaboration with community-based partner agencies, addresses a critical gap by identifying modifiable mechanisms impacting health and HRQOL over time. Utilizing 8 years of longitudinal survey data and objective data (biomarkers and physical and cognitive measures) and linking with administrative data from Centers for Medicare & Medicaid Services, the primary aims of the project are: 1) Identify at-risk LGBT older adults by investigating trajectories of health outcomes over time, their relationships with stigma, and the mediating roles of stress; 2) Understand modifiable mechanisms accounting for variability in changes in health outcomes by examining the roles of identity management, social networks, physical activity, and barriers to health care as well as health service utilization; and 3) Examine disparities in multimorbidity, disability, and HRQOL by demographic factors (age cohort, sex, gender identity, sexual orientation, and race/ethnicity) and risk and protective factors that account for health disparities. This study also harmonizes with external population-based data including Health and Retirement Study, National Health Interview Survey, and American Community Survey to enhance the study and ensure cost efficiency. As the older adult population increases, the health care costs associated with health disparities will continue to rise. To respond to this growing public health challenge it is imperative to identify groups at high risk of disparities and to determine the modifiable mechanisms impacting their health and well-being as they age. The findings from this research will generate much needed information to directly inform and guide the development of tailored interventions that can be effectively delivered within community- based agency settings to improve the health and quality of life of demographically diverse older adults.